常用SQL语句分享

前言:

日常工作或学习过程中,我们可能会经常用到某些SQL,建议大家多多整理记录下这些常用的SQL,这样后续用到会方便很多。笔者在工作及学习过程中也整理了下个人常用的SQL,现在分享给你!可能有些SQL你还不常用,但还是希望对你有所帮助,说不定某日有需求就可以用到。

注:下文分享的SQL适用于MySQL 5.7 版本,低版本可能稍许不同。有些SQL可能执行需要较高权限。

1.show相关语句

# 查看实例参数 例如:
show variables like '%innodb%';
show global variables like '%innodb%';

# 查看实例状态,例如:
show status like 'uptime%';
show global status like 'connection%';

# 查看数据库链接:
show processlist;
show full processlist;

# 查询某个表的结构:
show create table tb_name;

# 查询某个表的详细字段信息:
show full columns from tb_name;

# 查询某个表的全部索引信息:
show index from tb_name;

# 查询某个库以cd开头的表:
show tables like 'cd%';

# 查询某个库中的所有视图:
show table status where comment='view';

# 查询某个用户的权限:
show grants for 'test_user'@'%';

2.查看账户相关信息

# 这里先介绍下CONCAT函数:在MySQL中 CONCAT()函数用于将多个字符串连接成一个字符串,
利用此函数我们可以将原来一步无法得到的sql拼接出来,后面部分语句有用到该函数。
# 当拼接字符串中出现''时 需使用\转义符

# 查看所有用户名:
SELECT DISTINCT
    CONCAT(
        'User: \'',
        user,
        '\'@\'',
        host,
        '\';'
    ) AS QUERY
FROM
    mysql.user;

# 查看用户详细信息:
SELECT user,
    host,
    authentication_string,
    password_expired,
    password_lifetime,
    password_last_changed,
    account_locked 
FROM
    mysql.user;

3.KILL数据库链接

# 下面列举SQL只是拼接出kill 链接的语句,若想执行 直接将结果复制执行即可。
# 杀掉空闲时间大于2000s的链接:
SELECT
    concat( 'KILL ', id, ';' ) 
FROM
    information_schema.`PROCESSLIST` 
WHERE
    Command = 'Sleep' 
    AND TIME > 2000;
  
# 杀掉处于某状态的链接:
SELECT
    concat( 'KILL ', id, ';' ) 
FROM
    information_schema.`PROCESSLIST` 
WHERE
    STATE LIKE 'Creating sort index';
  
# 杀掉某个用户的链接:
SELECT
    concat( 'KILL ', id, ';' ) 
FROM
    information_schema.`PROCESSLIST` 
WHERE
    where user='root';

4.拼接创建数据库或用户语句

# 拼接创建数据库语句(排除系统库):
SELECT
    CONCAT(
        'create database ',
        '`',
    SCHEMA_NAME,
    '`',
    ' DEFAULT CHARACTER SET ',
    DEFAULT_CHARACTER_SET_NAME,
        ';'
    ) AS CreateDatabaseQuery
FROM
    information_schema.SCHEMATA
WHERE
    SCHEMA_NAME NOT IN (
        'information_schema',
        'performance_schema',
        'mysql',
        'sys'
    );
    
# 拼接创建用户语句(排除系统用户):
SELECT
    CONCAT(
        'create user \'',
    user,
    '\'@\'',
    Host,
    '\''
    ' IDENTIFIED BY PASSWORD \'',
    authentication_string,
        '\';'
    ) AS CreateUserQuery
FROM
    mysql.`user`
WHERE
    `User` NOT IN (
        'root',
        'mysql.session',
        'mysql.sys'
    );
# 有密码字符串哦 在其他实例执行 可直接创建出与本实例相同密码的用户。

5.查看库或表大小

# 查看整个实例占用空间大小:
SELECT
    concat( round( sum( data_length / 1024 / 1024 ), 2 ), 'MB' ) AS data_length_MB,
    concat( round( sum( index_length / 1024 / 1024 ), 2 ), 'MB' ) AS index_length_MB 
FROM
    information_schema.`TABLES`;
  
# 查看各个库占用大小:
SELECT
    TABLE_SCHEMA,
    concat( TRUNCATE ( sum( data_length )/ 1024 / 1024, 2 ), ' MB' ) AS data_size,
    concat( TRUNCATE ( sum( index_length )/ 1024 / 1024, 2 ), 'MB' ) AS index_size 
FROM
    information_schema.`TABLES`
GROUP BY
    TABLE_SCHEMA;
  
# 查看单个库占用空间大小:
SELECT
    concat( round( sum( data_length / 1024 / 1024 ), 2 ), 'MB' ) AS data_length_MB,
    concat( round( sum( index_length / 1024 / 1024 ), 2 ), 'MB' ) AS index_length_MB 
FROM
    information_schema.`TABLES`
WHERE
    table_schema = 'test_db';
  
# 查看单个表占用空间大小:
SELECT
    concat( round( sum( data_length / 1024 / 1024 ), 2 ), 'MB' ) AS data_length_MB,
    concat( round( sum( index_length / 1024 / 1024 ), 2 ), 'MB' ) AS index_length_MB 
FROM
    information_schema.`TABLES`
WHERE
    table_schema = 'test_db' 
    AND table_name = 'tbname';

6.查看表碎片及收缩语句

# 查看某个库下所有表的碎片情况:
SELECT
    t.TABLE_SCHEMA,
    t.TABLE_NAME,
    t.TABLE_ROWS,
    concat( round( t.DATA_LENGTH / 1024 / 1024, 2 ), 'M' ) AS size,
    t.INDEX_LENGTH,
    concat( round( t.DATA_FREE / 1024 / 1024, 2 ), 'M' ) AS datafree 
FROM
    information_schema.`TABLES` t 
WHERE
    t.TABLE_SCHEMA = 'test_db' 
ORDER BY
    datafree DESC;
  
# 收缩表,减少碎片:
alter table tb_name engine = innodb;
optimize table tb_name;

7.查找无主键表

# 查找某一个库无主键表:
SELECT
table_schema,
table_name
FROM
    information_schema.`TABLES`
WHERE
    table_schema = 'test_db'
AND TABLE_NAME NOT IN (
    SELECT
        table_name
    FROM
        information_schema.table_constraints t
    JOIN information_schema.key_column_usage k USING (
        constraint_name,
        table_schema,
        table_name
    )
    WHERE
        t.constraint_type = 'PRIMARY KEY'
    AND t.table_schema = 'test_db'
);

# 查找除系统库外 无主键表:
SELECT
    t1.table_schema,
    t1.table_name
FROM
    information_schema.`TABLES` t1
LEFT OUTER JOIN information_schema.TABLE_CONSTRAINTS t2 ON t1.table_schema = t2.TABLE_SCHEMA
AND t1.table_name = t2.TABLE_NAME
AND t2.CONSTRAINT_NAME IN ('PRIMARY')
WHERE
    t2.table_name IS NULL
AND t1.TABLE_SCHEMA NOT IN (
    'information_schema',
    'performance_schema',
    'mysql',
    'sys'
) ;

总结:

希望这些SQL语句能对你有所帮助,可以收藏一下,说不定某次就用到了呢!原创不易,感谢大家支持。

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